The invention relates to a device for ensuring the television compatability of picture sensors operating with opto mechanical analysis, said analysis being effected by the analyser of a camera using a serial or parallel-serial scanning of a field of view, comprising a digital device which serially supplies in digital form samples which are representative of elements of the field of view analyzed in chronological sequence, each sampled element being coded in p bits in parallel and a digital-to-analog converter, and also to display means in a television monitor (TV monitor) of the output signal of said digital-to-analog converter.
Said optomechanical analysis picture sensors to which the invention relates comprise mobile optical elements such as moving mirrors or rotating drums with mirrors, which are characterized by a high operating speed in the field and line scan and by a non-negligible associated inertia, which prevents their automatic positional control. To reproduce the picture thus analysed of a field of view, a TV monitor is used at present whose rates, that is to say whose field and line scanning frequencies are supplied by the analyser itself. This mode of operation has two drawbacks:
In the first place, the imperfections in the acquisition of the picture, which are caused by the mechanical sweeps, the latter having intrinsically slow response times, are retransmitted in their totality to the screen of the TV monitor; more specifically a fluctuation in the line synchronization, contractions or expansions of the picture because of angular velocities of the camera are concerned. On the other hand, it is desirable, especially for the sake of standardization, that it is possible to supply a picture signal of a precisely defined TV standard, for example the CCIR TV standard, instead of a TV signal whose standard is closely connected to one type or another of optomechanical analysis, and for which more specifically the line rates are not of TV standards. Obviating these two drawbacks forms at the same time a technical problem which the invention has for its object to resolve and for that purpose has for its aim to restore on a TV screen an improved picture which satisfies a TV standard.
The invention relates to cameras utilizing serial or parallel-serial scans, excluding cameras using parallel scanning, the preferred scanning mode being the parallel-serial scanning which, compared with serial scanning renders it possible, when scanning identical pictures or fields, to divide the rate of the line scan device by m, which reduces the line synchronization problems and renders it possible to use less fast photodetectors, by using a m times higher number of these photodetectors. When parallel-serial scanning is applied, the analog output signals of the camera are distributed in parallel over m conductors and a known and even conventional manner is to position, just downstream of the camera, a digital device which has also for its function to effect a scanning conversion, that is to say a conversion in the serial form of the picture lines in accordance with a chronological sequence which corresponds to the spatial sequence of the lines of the field of vision. Thus a serial line scan is obtained, the elements themselves being analysed serially in each line. Irrespective of the fact whether the scanning operation is effected in the serial or in the parallel-serial form, a sequence of digital samples in the serial form is then obtained at the output of the digital device, each sample being representative of an element, coded in parallel over p bits. In this request it should be noted that the number m does not occur to make the invention effective nor to optimize its embodiments, all this occurring as if the digital device is integrated in the camera and in all these cases a serial scan being concerned. In accordance with the known technique, the output signal of the digital member can be applied to the TV monitor after having been converted by a digital-to-analog converter and, optionally via a digital processing module in which different types of filtering operations or processing operations such as concatenation, convolution or the elimination of the background of a scene can be effected. In accordance with this technique, the above-mentioned imperfections in the picture on the TV monitor continue, particularly the fluctuations in the line synchronization which is caused by faults in the sensor of the line analyser and various parasitics such as electrical or mechanical disturbances, dust or other causes. On the other hand, the total number of lines per picture is generally equal to a multiple k of m for the case of an analysis on bands having m lines, for example: k.times.m=57.times.11=627 lines; finally the line and field synchronizations are imperfect because of moves by the carrier of the camera. The above-mentioned imperfections cannot be corrected for principle reasons or because of technological limitations.
A known mode of operation consists in giving the analyser a picture frequency which is identical to that of the TV receiver used, and the standard of the latter. This mode of operation is known from, for example, United Kingdom Patent Specification GB 1,482,789 but which is used in a technical field which differs from that of the invention, for a camera using parallel analysis, that is to say a field in which the line synchronization is not a problem. It will be noted that furthermore in this known technique a memory must be provided whose capacity is higher than or equal to a field to ensure the conversion of the standard searched, that is to say several hundreds of lines, which in the state of the art is complicated and expensive and introduces a considerable delay between the analysis and the display.